Method for preventing a metal corrosion in a semiconductor device

ABSTRACT

The present invention relates to a method for preventing a metal corrosion in a semiconductor device. The present method includes the steps of etching of a metal layer in a chamber, the metal layer having a photoresist pattern thereon or thereover; oxidizing a surface of the metal layer using a plasma comprising N 2 O in the same chamber; and removing the photoresist. Therefore, metal corrosion as well as bridges between metal wirings can be suppressed or prevented, thereby improving the profile of metal layer and the reliability and yield of the semiconductor device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor device manufacturingtechnology. More specifically, the present invention relates to a methodfor preventing corrosion of a metal layer in a semiconductor device,thereby enabling improvement of the reliability and yield of asemiconductor device.

2. Description of the Related Art

Following the rapid progress of information and communication media suchas a computer, the technology of manufacturing a semiconductor devicehas been rapidly developed. A semiconductor device has been developedtoward higher integration, miniaturization, and higher operationalspeed.

Currently, aluminum or aluminum alloys are widely used as a wiringmaterial for integrated circuits such as VLSI (Very Large-ScaleIntegration) devices, because of their superior electric conductivityand low prices. Processes of forming aluminum wiring generally comprisethe steps of: forming an aluminum layer; coating and patterning aphotoresist on the aluminum layer; etching an exposed portion of thealuminum layer (i.e., which is not covered with the photoresist) bymeans of plasma including chlorine; and removing the photoresist.

FIGS. 1 a to 1 c are cross-sectional views of a semiconductor deviceillustrating a conventional method for forming an aluminum wiring in thesemiconductor device.

First, as shown in FIG. 1 a, a photoresist is coated and patterned overa substrate 100 on which an oxide layer 102, barrier 104, aluminum layer106 and antireflective coating 108 are formed in due order. Then, theantireflective coating 108, aluminum layer 106 and barrier 104 aredry-etched by means of Reactive Ion Etching (RIE) using a chlorinesource gas such as Cl₂, BCl₃ and the like. Here, the patternedphotoresist 110 is used as a mask for this etching process.

Next, as shown in FIG. 1 b, the patterned photoresist 110 is removed bymeans of O₂ plasma ashing process. At this time, corrosion defects 112on a surface of aluminum layer 106 may result from circumstances such asfluorine, NH₄OH, water, etc., working conditions of RIE, cleaningsolutions used for removal of a photoresist, and especially chlorineresidues occurring during the etch of aluminum layer 106. The corrosiondefects 112 deteriorate the electrical performance of the semiconductordevice or integrated circuit, or cause failures such as a short circuitthus decreasing the yield of manufacturing the semiconductor device.

In order to prevent such corrosion defects, the following methods areconventionally used. A first method involves cleaning the chlorineresidues using deionized water, usually as a spray or in a bath. Asecond method involves evaporating the chlorine residues by heattreatment. A third method involves using a plasma containing fluorine.

However, the first method has little effect on removal of the chlorineresidues, and generally does not prevent the corrosion of aluminumwirings in the long run. The second method may produce or result inproblems such as hillock formation, segregation, or recrystallization,etc. when the temperature of the heat treatment is over 300° C., whichare generally related to the low melting point of aluminum.

The third method has been disclosed in Japanese Patent Publication No.83-12343 and Korean Patent Laid-Open Publication No. 2000-27241, whichrelates to a method for removing chlorine residues by means of anetching gas containing fluorine, and then removing a photoresist throughan ashing process. However, this method may result in a problem whereundercuts 114 on a titanium-containing layer (e.g., a TiN or TiWbarrier) occur due to the fluorine-containing plasma, as shown in FIG. 1c. In addition, an underlying oxide layer may be damaged, and thealuminum may be changed to AlF₃ (which can result in metal degradation).As a result, the reliability of semiconductor device may beconspicuously deteriorated.

In another method for manufacturing a semiconductor device, for thepurpose of preventing reaction between chlorine residues and water whena substrate is exposed to air, an etching system is equipped with anashing chamber so that a process of stripping a photoresist is performedin situ. Especially, before stripping a photoresist by means of plasmacontaining fluorine, chlorine residues are changed to hydrogen chloride(HCl) by means of H₂O plasma, and then hydrogen chloride is exhausted bya pump, so that chlorine residues existing on surfaces of aluminum layerare generally removed. However, there are the same problems as theabove-explained method has, which are caused by plasma containingfluorine.

To solve these problems, Korean Patent Publication No. 95-5351 disclosesa method for preventing corrosion of a metal layer, comprising a plasmaprocess using mixed gases of oxygen (O₂) and ammonia (NH₃). In addition,Korean Patent Laid Open Publication No. 2001-35852 discloses a methodfor preventing corrosion of a metal layer, comprising the step ofexposing an object to plasma formed of mixed gases of H₂N₂ and oxygen.However, in case of using such mixed gases, a degree of preventingcorrosion of a metal layer depends on a mixture ratio of gases.Moreover, these methods tend to have little effect on the prevention ofcorrosion.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a methodfor preventing metal corrosion in a semiconductor device (and, in oneembodiment, simultaneously preventing formation of a bridge betweenmetal wirings), thereby improving the profile of metal layer and thereliability and yield of the semiconductor device.

To achieve the above object(s), a method for preventing metal corrosionof a metal layer in a semiconductor device or integrated circuitaccording to the present invention comprises the steps of: etching ametal layer in a chamber, the metal layer having a photoresist patternthereon or thereover; oxidizing a surface of the metal layer using aplasma comprising N₂O in the chamber; and removing the photoresist.

Preferably, the present method further includes the step of removing aportion of the oxidized metal surface by sputter etching using an inertgas, after the step of oxidizing the surface of the metal layer. Theinert gas includes at least one member of the group consisting of He,Ne, Ar, Kr, Xe and Rn. Also, the metal layer preferably comprises one ormore layers consisting essentially of aluminum or an aluminum alloy(e.g., aluminum-copper or aluminum-silicon alloy).

The etch of the metal layer may be performed by dry etching using aplasma which includes chlorine. In addition, after the metal layer isetched, the metal layer may have a width greater than a desired orpredetermined critical dimension by 50 to 150 Å. Further, the oxidizedmetal surface may have a width or thickness of from 50 to 150 Å.

In addition, the step of removing the photoresist preferably comprisesashing with a plasma including a chlorine source gas (e.g., Cl₂) and ahydrofluorocarbon gas (e.g., CHF₃).

These and other aspects of the invention will become evident byreference to the following description of the invention, often referringto the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 a to 1 c illustrate a conventional method for forming analuminum wiring in a semiconductor device.

FIGS. 2 a to 2 d illustrate a method for preventing corrosion of a metallayer in a semiconductor device, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 a to 2 d are cross-sectional views of a semiconductor deviceillustrating a method for preventing a metal corrosion according to thepresent invention.

First, as shown in FIG. 2 a, a photoresist 210 is coated and patternedover a substrate 200 on which an oxide layer 202, barrier 204, metallayer 206 and antireflective coating 208 are formed in successive order.Then, antireflective coating 208, metal layer 206 and barrier 204 aredry-etched using a plasma including a chlorine source gas such as Cl₂,BCl₃ and/or the like. Such dry etching preferably comprises Reactive IonEtching (RIE).

Metal layer 206 may comprise a single layer or a plurality of layers, atleast one of which preferably consists essentially of aluminum, aluminumalloy (for example, Al—Cu or Al—Ti), aluminum-silicon alloy (forexample, Al—Si, Al—Si—Cu, or Al—Ti—Si), and so on. However, materialsare not limited to these metals or alloys thereof, and any metal oralloy thereof is available for the metal layer 206 in the presentinvention.

In case a metal layer 206 comprises aluminum, an aluminum layer may beweak for electromigration because aluminum has a relatively low meltingpoint of around 660° C. As a result, atoms of aluminum may be apt tomove due to movement of electrons. Preferably, in order to preventelectromigration, a barrier 204 comprising or consisting essentially ofTi, TiN, W or TiW can be formed under an aluminum layer. In oneembodiment, barrier 204 consists essentially of a Ti/TiN bilayer.Furthermore, in case a metal layer 206 comprises aluminum, anantireflective coating 208 comprising or consisting essentially of TiNor a Ti/TiN bilayer is preferably formed on the aluminum layer 206,which can suppress or prevent hillock formation, electromigration andstress migration of the aluminum layer 206, thus improving thereliability of the wiring. Barrier 204 and antireflective coating 208are optional components, not indispensable components.

A width W of a metal layer 206 is preferably wider than the desired (orpredetermined) critical dimension by 50 to 150 Å. Generally, that widthcorresponds to or is considered for a thickness of a lateral metal oxideto be formed in a subsequent process (e.g., plasma oxidation). In aconventional etching process, metal layer 206 may be overetched to alimited extent. However, in this embodiment according to the presentinvention, metal layer 206 is not overetched, so that portions of oxidelayer 202 below metal layer 206 are not etched.

Next, as shown in FIG. 2 b, a surface of metal layer 206 (e.g., exposedas a result of the metal etching step) is oxidized using a plasmacomprising N₂O. The oxidation may be performed in the same chamber asthe etching process for metal layer 206. Thus, the metal etch andoxidation steps may be performed continuously, or oxidation may beconducted in situ. During such an oxidization process, lateral surfacesof a metal layer 206 are oxidized so that lateral oxides 212 are formed.The lateral oxides 212 may have a width (or thickness) of from around 50Å to around 150 Å. Chlorine residues remaining or existing on lateralsurfaces of metal layer 206 after the metal etch step are oxidized andremoved by the N₂O-containing plasma. In order to effectively remove thechlorine residues, the present method further includes the steps of:exposing metal surfaces that may have chlorine residues thereon to anH₂O-containing plasma before oxidization using the N₂O-containingplasma, so as to change the chlorine residues to hydrogen chloride (orother volatile species); and exhausting the hydrogen chloride and/orother volatile, chlorine-containing species.

Next, as shown in FIG. 2 c, a sputter etch process or ion beam etchprocess is performed. Sputter etching or ion beam etching is a methodfor physically etching a target by means of accelerating ions in aplasma state which are changed from an inert gas. In this process, aportion of lateral oxides 212 is removed (e.g., the vertically exposedportions of lateral oxides 212) and a portion of oxide layer 202 is alsoetched at the same time. Thus, the formation of a bridge (or shortcircuit between adjacent metal lines, sometimes known as a “stringer”)can be suppressed or prevented, thereby improving a profile of metallayer 206. Moreover, a photoresist 210 is partially removed. It ispreferable that the inert gas comprises at least one of the noble gases(i.e., He, Ne, Ar, Kr, Xe and Rn).

Finally, as shown in FIG. 2 d, photoresist 210 is removed. Preferably,the removal of photoresist 210 comprises a plasma ashing process using achlorine source gas (e.g., Cl₂, BCl₃, HCl, etc., preferably Cl₂) and ahydrofluorocarbon gas (e.g., C_(x)H_(y)F_(z), where x is an integer offrom 1 to 4, y and z are each an integer of at least 1, and (y+z)=2x+2,such as CHF₃, CH₂F₂, C₂H₂F₄, C₂HF₅, etc., preferably CHF₃). In addition,it is preferable that the chamber for forming the ashing plasma hasworking conditions of: a pressure of from about 0.7 to about 1.3 Torr;an electric power of from about 800 to about 1700 W; an operating timeof from about 20 to about 80 seconds; and a temperature less than roomtemperature.

It is also preferable that the above-described series of processes, fromthe metal etch step as shown in FIG. 2 a to the photoresist removal stepas shown in FIG. 2 d, are continuously performed in the same etchingchamber.

The above-described embodiment according to the present invention hasexplained a series of processes, comprising the steps of: etching ametal layer in a chamber, the metal layer having thereon or thereover apredetermined photoresist pattern; oxidizing surfaces of the metal layerusing a N₂O-containing plasma; removing a portion of the oxidized metallayer surfaces and simultaneously etching an exposed oxide layer bysputter etching using an inert gas; and removing the photoresist byplasma ashing. However, the step of sputter etching using an inert gasmay be omitted. Namely, the method according to the present inventionmay comprise the following steps of: etching a metal layer under aphotoresist pattern; oxidizing surfaces of the metal layer with a plasmacomprising N₂O; and removing the photoresist by plasma ashing.

In a method for preventing a metal corrosion in a semiconductor deviceor integrated circuit according to the present invention, a metal layeris dry-etched, lateral oxides are formed using a N₂O-containing plasmain situ, and then portions of the lateral oxides and an oxide layer(exposed as a result of the metal etch) are simultaneously removed bysputter etching using an inert gas. Therefore, metal corrosion andbridges (a type of short circuit between adjacent metal lines) can besuppressed or prevented, improving a profile of the metal layer.Moreover, undercuts into a barrier layer, damage to an oxide layerand/or deformation of the metal layer can be suppressed or prevented. Asa result, the present invention may improve the reliability and yield ofa semiconductor device.

While the present invention has been shown and described with referenceto certain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A method for preventing metal corrosion in a semiconductor orintegrated circuit, comprising the steps of: forming an oxide layer on asubstrate; forming a metal layer on the oxide layer; etching the metallayer in a chamber to expose a surface of the oxide layer, the metallayer having a photoresist pattern thereon or thereover; oxidizinglateral surfaces of the metal layer using a plasma comprising N₂O in thechamber to form lateral metal oxides; removing simultaneously a portionof the oxide layer exposed by etching the metal layer and verticallyexposed portions of said lateral metal oxides by sputter etching with aninert gas in the chamber, and removing the photoresist.
 2. The meted ofclaim 1, wherein the inert gas includes at least one member of the groupconsisting of He, Ne, Ar, Kr, Xe and Rn.
 3. The method of claim 1,wherein the metal layer comprises one or more aluminum layers consistingessentially of aluminum or aluminum alloy.
 4. The method of claim 3,wherein the one or more aluminum layers consists essentially of analuminum alloy selected from the group consisting of aluminum-copper,aluminum-titanium, and aluminum-silicon alloys.
 5. The method of claim3, wherein the aluminum alloy is selected from the group consisting ofaluminum-copper and aluminum-copper-silicon alloys.
 6. The method ofclaim 3, wherein the metal layer further comprises one or more barrierlayers.
 7. The method of claim 6, wherein the one or more barrier layerscomprises a Ti, TiN, W or TiW layer.
 8. The method of claim 7, whereinthe one or more barrier layers comprises a Ti/TiN bilayer.
 9. The methodof claim 3, wherein the metal layer further comprises an antireflectivecoating.
 10. The method of claim 9, wherein the antireflective coatingcomprises a TiN layer.
 11. The method of claim 9, wherein theantireflective coating comprises a Ti/TiN bilayer.
 12. The method ofclaim 1, wherein etching the metal layer comprises dry etching with aplasma comprising chlorine.
 13. The method of claim 12, wherein the dryetching comprises reactive ion etching (RIE).
 14. The method of claim 1,wherein the metal layer has a width 50 to 150 Å greater than a desiredor predetermined critical dimension after the metal layer is etched. 15.The method of claim 1, wherein the oxidized metal surface has a width offrom 50 to 159 Å.
 16. The method of claim 1, wherein the step ofremoving the photoresist comprises ashing with a plasma comprising achlorine source gas and a hydrofluorocarbon gas.
 17. The method of claim1, wherein the step of removing the photoresist comprises ashing with aplasma comprising Cl₂ and CHF₃ gases.
 18. The method of claim 6, whereinthe one or more barrier layers are under the metal layer.
 19. The methodof claim 9, wherein the antireflective coating is on the metal layer.